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Published online ahead of print on 17 September 2009 as doi:10.1099/mic.0.031021-0
Microbiology (2009), DOI 10.1099/mic.0.031021-0
© 2009 Society for General Microbiology
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Microbiology 0 (2009), mic.0.031021; DOI  10.1099/mic.0.031021-0
© 2009 Society for General Microbiology

RelA regulates virulence and intracellular survival of Francisella novicida

Rachel E. Dean1,3, Philip M. Ireland1, Janine E. Jordan1, Richard W. Titball2 and Petra C.F. Oyston1

1 Dstl Porton Down;
2 University of Exeter

Analysis of the genome of Francisella tularensis revealed few regulatory systems and how the organism adapts to conditions in different niches is poorly understood. The stringent response is a global stress response mediated by (p)ppGpp. The enzyme RelA has been shown to be involved in generation of this signal molecule in a range of bacterial species. We investigated the effect of inactivation of the relA gene in Francisella by generating a mutant in Francisella novicida. Under amino acid starvation conditions, the relA mutant was defective for (p)ppGpp production. Characterisation showed the mutant to grow similarly to the wild type, except that it entered stationary phase later than wild type cultures, resulting in higher cell yields. The relA mutant showed increased biofilm formation which may be linked to the delay in entering stationary phase which would result in higher cell numbers present in the biofilm, and reduced resistance to in vitro stress. The mutant was attenuated in the J774A macrophage cell line and was shown to be attenuated in the mouse model of tularaemia, but able to induce a protective immune response. Therefore, (p)ppGpp appears to be an important intracellular signal, integral to the pathogenesis of F. novicida.

3 E-mail: redean{at}dstl.gov.uk






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